Reversible transference of Au nanoparticles across the water and toluene interface: A Langmuir type adsorption mechanism

A novel method to reversibly modify the surface of gold nanoparticles is de veloped through electrostatic interaction between cationic tetraoctylammoni um surfactant and anionic carboxylate groups. The particles can be extracte d from the water phase into the toluene phase without aggregation after the adsorption of the surfactant on their surface. UV-visible spectroscopy rev eals that a Langmuir type adsorption isotherm is observed during the transf erence process. The maximum adsorption amount of surfactants is equal to th e total amount of carboxylate groups on the particle surface, indicating th at the saturation adsorption behavior consistent with the;langmuir isotherm is solely caused by the 1:1 electrostatic charge interaction. Furthermore, through adjusting the dissociation states of carboxylate groups on the par ticle surface using hydrochloric acid, it is possible to redisperse the par ticles from toluene into the water layer because of the desorption of TOAB molecules from the particle surface. Studies using other methods such as in frared spectroscopy; energy-dispersive X-ray analysis, and transmission ele ctron spectroscopy also support the above findings.